A patient developed proptosis and diplopia of 2 months duration following injury. On examination there is chemosis, conjunctival redness, and external ocular nerve palsy. Investigation of choice is:
**Core Concept**
The patient's symptoms of proptosis (bulging eye), diplopia (double vision), chemosis (swelling of the conjunctiva), conjunctival redness, and external ocular nerve palsy suggest a diagnosis of orbital cellulitis or a more sinister condition like carotid-cavernous fistula (CCF) or orbital apex syndrome. These conditions often result from trauma, which may have compromised the orbital or cavernous sinus structures.
**Why the Correct Answer is Right**
The investigation of choice is **MRI with contrast**. This is because MRI can provide detailed images of the soft tissues and bones of the orbit, including the orbital apex, cavernous sinus, and surrounding structures. Contrast-enhanced MRI can help identify the presence of an abnormal vascular connection (fistula) or an abscess, which may be responsible for the patient's symptoms. The high sensitivity and specificity of MRI make it an ideal diagnostic tool for evaluating complex orbital and cavernous sinus pathology.
**Why Each Wrong Option is Incorrect**
**Option A:** CT scan of the orbit without contrast may not provide sufficient information to diagnose complex conditions like CCF or orbital apex syndrome. Contrast-enhanced CT might be more helpful, but MRI remains the gold standard.
**Option B:** Angiography may be useful in diagnosing vascular abnormalities like CCF, but it is not the first-line investigation for orbital cellulitis or orbital apex syndrome.
**Option C:** Ultrasound may be useful for detecting orbital masses or abscesses, but it lacks the sensitivity and specificity of MRI for complex orbital and cavernous sinus pathology.
**Clinical Pearl / High-Yield Fact**
In cases of suspected orbital apex syndrome or carotid-cavernous fistula, it's essential to perform a thorough evaluation of the patient's visual acuity, visual fields, and pupillary reactions to assess the extent of optic nerve involvement.
**Correct Answer:** C. MRI with contrast.